Morphology controlled synthesis of Fe and Mn co-doped In2O3 nanocubes and their Dopant-Atom effects on electronic structure and magnetic properties

Abstract

Fe and Mn co-doped In2O3 single-phase cubic crystal structure nanocubes of uniform size and control over dopant concentration (In1.96Fe0.02Mn0.02O3, In1.94Fe0.02Mn0.04O3, In1.92Fe0.02Mn0.06O3 and In1.90Fe0.02Mn0.08O3) and microstructure were prepared using the hydrothermal-annealing technique. On a wider vision, we systematically investigated the influence of Fe and Mn co-doping in In2O3 through complementary experimental techniques and density functional theoretical (DFT) calculations to reveal the physical mechanisms involved in the origin of observed ferromagnetism. DFT calculations demonstrated that the substitution of surface indium atom by iron (FeIn) leads to impurity states on the top of In2O3 valence band maximum (VBM). Conversely, incorporation of interstitial (Mni) impurities in the host matrix without oxygen vacancies (VO) slightly shifts the top of the valence band and incorporation of interstitial Mn-impurity in the In2O3 (111) surface with oxygen vacancy does not provide noticeable changes in the electronic structure of the defective surface. High-resolution transmission electron microscopy measurements showed the formation of regular nanocubes in shape with 36.9–37.6 nm in average edge length. X-ray photoelectron spectroscopy investigations revealed that valence state of Fe mostly as Fe2+ and Fe3+ and Mn2+ for Mn atom in the In1.96Fe0.02Mn0.02O3, In1.94Fe0.02Mn0.04O3, In1.92Fe0.02Mn0.06O3 and In1.90Fe0.02Mn0.08O3. Magnetic studies exhibited room temperature ferromagnetism (RTFM) in the investigated samples with the high coercivity and saturation magnetization of 145.48 Oe and 0.023 emu/g, respectively for the In1.94Fe0.02Mn0.04O3. The origin of observed RTFM was described based on the bound magnetic polaron (BMP) model mechanism. DFT investigations demonstrated the clusters of impurities (FeIn-nMni) robust magnetic interactions within the cluster and between the clusters. Interestingly, only FeIn-nMni clusters contribute ferromagnetism observed in the investigated co-doped systems. Therefore, increasing the concentration of defects leads to the improvement of ferromagnetism. The comprehensive experimental and DFT investigations present new evidence to the observed ferromagnetism and electronic structure of Fe,Mn co-doped In2O3 nanocubes.